1. Field of the Invention
This invention relates to a display control method and apparatus and, more particularly, to a display control method and apparatus for quantizing input data to binary or multivalued data and delivering the quantized data to a display device such as a matrix panel display.
2. Description of the Related Art
Examples of matrix panel displays according to the prior art include plasma displays, electroluminescence displays and liquid-crystal displays. Among these the liquid-crystal display is used most widely owing to its clarity and low power consumption.
One type of liquid-crystal display is a ferrodielectric liquid-crystal display (hereinafter referred to an "FLC"), in which the liquid crystal differs from other types of liquid crystal in that it exhibits a "memory" property. Specifically, the liquid crystal retains the state of a display changed by application of an electric field. In a display device using an FLC, the memory property assures that there is no decline in contrast regardless of the number of scanning lines. This makes it possible to provide a large-screen, high-definition display.
The above-mentioned FLC is an element capable of displaying only two values (two gray levels). Consequently, in order to express half tones, a technique often used is to split a pixel into a plurality of pixels. With this method, however, tones can only be expressed in a stepwise manner. This method falls far short of full-color or analog tones and is not suited to display of photographs, for example.
The dither method and error-diffusion method are known as methods of expressing full-color and analog tones from a small number of tones.
The dither method is effective in displays having a certain number of gray levels. However, in displays of two, three or four grays, a satisfactory picture quality cannot be obtained. The error-diffusion method provides better picture quality than the dither method and makes it possible to obtain a satisfactory picture quality even with a display of two grays. However, since a property of the error-diffusion method is that error is diffused to nearby pixels, processing that is continuous at all times is required. Accordingly, interlace scanning in which scanning is performed every other line cannot be carried out in a display.
With an FLC, however, a fixed period of time is needed to write one line. If the number of scanning lines is large, therefore, the frame frequency declines. In interlace scanning in which scanning is performed in regular order from the top to the bottom of the display screen, this leads to image flicker and results in a display which does not have a quick response.
In a display device using an FLC, therefore, it is necessary to use "multi-interlacing" or "partial preferential scanning". In multi-interlacing, scanning is performed while skipping a plurality of lines. In FIG. 11, for example, a display is shown in which skipping is performed every two lines. In partial preferential scanning, the scanning lines of that portion of an image that has changed from the immediately preceding frame of the image are scanned preferentially.
Accordingly, it is difficult to use image processing requiring continuous processing, such as the aforementioned error-diffusion method, in an FLC display that requires multi-interlacing or partial preferential scanning.